The relief resulting from the successful launch of Space Shuttle Discovery after a 2-1/2 year re-engineering effort following the Columbia disaster has been quickly replaced by dismay. Before the shuttle even reached the International Space Station, NASA had announced that the shuttle fleet would again be grounded. Although the craft seems not to have been damaged by foam shed from the external fuel tank, design changes were unable to keep a piece of foam, estimated to weigh about a pound, from coming loose during the ascent to orbit. Clearly, NASA is beginning to worry that there may be no economic solution to the problem of foam coming loose from the big fuel tank.
The space shuttle and its launch system are increasingly beginning to seem fragile. Some of their vulnerabilities result from a major early design decision. Unlike other objects we have launched into orbit, the space shuttle sits not atop the rockets that propel it, but beside them. This tends to make propulsion system failures catastrophic (as in the case of Challenger), and it puts the vulnerable thermal tiles of the shuttle in harm’s way of insulation that breaks off the external fuel tank. If the shuttle sat on top of the rockets that propel it, rocket engine failures—even rocket explosions—might be survivable. And, of course, the shedding of foam insulation would be completely innocuous.